Ian Hart, left, will play Dr. Franklin Hall -- the civilian identity of Marvel supervillain Graviton -- on ABC's "Agents of S.H.I.E.L.D."

The official synopsis for "Marvel's Agents of S.H.I.E.L.D." third episode reveals that an established Marvel character will join the show: Dr. Franklin Hall, better known in comic book lore as supervillain Graviton.

The character will be played by Ian Hart, of "Luck" and "Dirt." When his involvement with the show was first announced last month, he was said to be playing a recurring role, though there's no indication yet that he'll appear under the Graviton name, or have the character's gravity-controlling superpowers.

The description for the episode, "The Asset," doesn't mention Hall's supervillain alter ego: "When the brilliant scientist, Dr. Franklin Hall, is kidnapped, Agent Coulson and his S.H.I.E.L.D. agents must race against the clock to locate him. Skye is their only way in -- pushing the team to their limits when the entire plan turns upside-down."

Graviton first appeared in 1977's "Avengers" #158, and has made appearances in "West Coast Avengers," "Thunderbolts" and, most recently, "Secret Avengers." Though prior speculation that the character played by J. August Richards in the show's pilot was Luke Cage was unfounded, this news signals that "Agents of S.H.I.E.L.D." is willing to adapt preexisting Marvel characters, along with it's original-to-live-action main cast.

"The Asset," written by showrunners Jed Whedon and Maurissa Tancharoen and directed by David Solomon, is scheduled to air Oct. 8. "Marvel's Agents of S.H.I.E.L.D.," set in the same fictional world as the Marvel Studios film franchise, makes its series debut Tuesday, Sept. 24 on ABC.